1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a method of bonding an ethylenexe2x80xa2xcex1-olefin rubber composition and a fiber for use in a power transmission belt. The invention also relates to a power transmission belt resulting from the practice of the method.
2. Background Art
Increasing demand for energy saving has led to more compact automotive designs. Engine compartments have become increasingly smaller, as a result of which the engines are required to operate in relatively high temperature environments. Power transmission belts used on these engines are required to perform reliably in these high temperature environments.
Heretofore, natural rubber, styrene-butadiene rubber, and chloroprene rubber have been used predominantly in the construction of power transmission belts. These rubbers, used in a compression rubber layer of a power transmission belt, are prone to cracking prematurely when they are operated in high temperature environments, such as in confined automobile engine compartments.
To address this problem of premature failure, studies have been undertaken to improve the heat resistence of chloroprene rubber. Ethylenexe2x80xa2xcex1-olefin elastomers, such as ethylene-propylene rubber (EPR) and ethylene-butadiene-diene rubber (EPDM), have recently been proposed for use in power transmission belts in place of chloroprene rubber. These polymers are desirable in that they exhibit good heat and cold resistence and are generally economical to use. Use of these polymers is disclosed, for example, in Japanese Unexamined Patent Application No. 6-345948.
However, EPR has a relatively low tear strength, which may decrease even further in a peroxide vulcanization system. These belts are prone to popping out during operation. On the other hand, with a sulfur vulcanization system, it may be difficult to impart a sufficient degree of vulcanization to the rubber, as a result of which the belt may wear significantly during operation. This wear is particularly a problem when using a V-ribbed belt construction in which dust accumulates at the bottom of pulley recesses between adjacent ribs. This may result in tack wear which may in turn account for significant, unwanted noise generation. To increase the degree of vulcanization, EPDM with a very high number of double bonds in the molecules may alleviate tack wear to a certain extent. However, at the same time, it tends to reduce heat resistence of the rubber.
Another problem in the power transmission belt art relates to the bonding of an ethylene-xcex1-olefin elastomer with a fiber cord. It is known, as disclosed in Japanese Unexamined Patent Application Publication No. 8-113657, to immersion treat a fiber material with a dipping solution made up of a resorcinol-formalin-styrene-butadiene-vinyl pyridine latex which is vulcanization bonded to an EPDM rubber composition. It is also known, as disclosed in Japanese Unexamined Patent Application Publication No. 8-113656, to adhesion treat fiber with a solution made up of a resorcinol-formalin rubber latex. The fiber is then vulcanization-bonded to an EPDM rubber composition made up of a methylene donor, a methylene acceptor, and a silicic acid compound.
While using a dipping solution of a resorcinol-formalin-styrene-butadiene-vinyl pyridine latex to treat the fiber material results in improved bonding strength, it may compromise other performance characteristics. With the fiber material used in load carrying cords in a transmission belt, repeated flexing may cause the load carrying cords to prematurely peel from the rubber layer in which they are embedded. This may also be true of fiber material treated with an EPDM rubber composition made up of a methylene donor, a methylene acceptor, and a silicic acid compound, when the fiber material is used in a power transmission belt as a component which is repeatedly flexed.
Because of environmental concerns, ethylenexe2x80xa2xcex1-olefin rubber compositions have been preferred as polymers because they contain little or no pollutant. As a result, various ethylenexe2x80xa2xcex1-olefin rubber compositions have been used. However, most of these compositions contain a halogenated polymer, which is an environmental pollutant. In view of this problem, there has been a demand for a method of bonding a halogenated polymer-free ethylenexe2x80xa2xcex1-olefin rubber composition to a fiber material.
In one form, the invention is directed to a method of bonding an ethylenexe2x80xa2xcex1-olefin rubber composition with a fiber material. The method includes the steps of adhesion treating the fiber material with a resorcinol-formalin-rubber latex with an ethylenexe2x80xa2xcex1-olefin elastomer latex and vulcanization bonding the adhesion-treated fiber material together with an unvulcanized ethylenexe2x80xa2xcex1-olefin rubber composition.
The method may further include the step of overcoat treating the adhesion treated fiber material with a rubber adhesive solution prepared by dissolving an unvulcanized ethylenexe2x80xa2xcex1-olefin rubber composition in a solvent before vulcanization bonding.
In one form, the sum of the diene content in ethylenexe2x80xa2xcex1-olefin rubber used for the resorcinol-formalin-rubber latex and the diene content in ethylenexe2x80xa2xcex1-olefin rubber used for the overcoat treating solution is at least 15%.
In one form, the solid pickup of the overcoat treating solution is within the range of 1-12% by weight.
The method may further include the step of adhesion treating the fiber material with a pre-treating solution made up at least one of (a) an isocyanate compound and (b) an epoxy compound before adhesion treating the fiber material with the resorcinol-formalin-rubber latex.
The method may further include the step of overcoat treating the fiber material with a rubber adhesive solution prepared by dissolving an ethylenexe2x80xa2xcex1-olefin rubber composition in a solvent before the vulcanization bonding step.
The method may further include the step of overcoat treating the fiber material with a solution prepared by adding 5-30% by weight of carbon black to a resorcinol-formalin-rubber latex consisting of an ethylenexe2x80xa2xcex1-olefin elastomer latex before the vulcanization bonding step.
In one form, the molar ratio of resorcinol to formalin is within the range of 1:2 to 2:1 in the resorcinol-formalin-rubber latex. The mass ratio of resorcinol-formalin precondensate to rubber latex may be within the range of 1:2 to 1:8 in the overall solid content.
The method may further include the step of incorporating the fiber material into a power transmission belt.
The fiber material may be a load carrying element, such as a load carrying layer or cord.
The invention is also directed to a power transmission belt having a body with a length. The body has a fiber material extending lengthwise of the belt body, with the fiber material being adhesion-treated with a resorcinol-formalin-rubber latex consisting of an ethylenexe2x80xa2xcex1-olefin elastomer latex. The fiber material may thereafter be vulcanization bonded together with an unvulcanized ethylenexe2x80xa2xcex1-olefin rubber composition.
The fiber material may be a load carrying element, such as a cord.
The fiber material may be embedded in a rubber layer consisting of an ethylenexe2x80xa2xcex1-olefin elastomer.
The fiber material may be overcoat treated with a rubber adhesive solution prepared by dissolving an unvulcanized ethylenexe2x80xa2xcex1-olefin rubber composition in a solvent.
In one form, the sum of the diene content in ethylenexe2x80xa2xcex1-olefin rubber used for the resorcinol-formalin-rubber latex and the diene content in ethylenexe2x80xa2xcex1-olefin rubber used for the rubber adhesive solution is not less than 15% by weight.
In one form, the ethylenexe2x80xa2xcex1-olefin rubber composition consists of at least one of (a) a rubber derivable from an ethylene-propylene-diene monomer and (b) EPR.
The fiber material may be at least one of (a) polyester fiber, (b) polyethylene terephthalate fiber, and (c) polyethylene naphthalate fiber.